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When night fell, the doctor came to check on a few people and prescribe medicine for treatment, but Uchiha Nagi signaled him not to bother, as he was a doctor himself.
The Mystical Palm Technique immediately activated, and green Chakra instantly healed a wound.
Tanjiro and the others were stunned by the sight.
Tanjiro, unable to keep his thoughts to himself, immediately asked, "Nagi-aniki (Nagi, older brother), if you can heal, why didn't you help us on the mountain just now?"
Uchiha Nagi shook his head. "The Mystical Palm Technique uses Chakra to rapidly promote human cell growth, but the number of times human cells can divide in a lifetime is limited. Rapidly promoting their division is actually not very good. If there's no life-threatening danger, it's best for the body's injuries to heal naturally; that's the ideal way."
"Moreover, you are still in your adolescent growth phase. Overusing the Mystical Palm Technique consumes your cells' regenerative power, which is equivalent to consuming your potential."
Tanjiro, who could sense a person's emotions, knew that Uchiha Nagi wasn't lying, so he nodded.
"I see, I understand. Oh, by the way, Nagi-aniki (Nagi, older brother), I've been trying to refine that Chakra you mentioned for several days, but I can't find a clue. Could you explain it to me again?"
"Hmm, I can—" Uchiha Nagi nodded.
"What is Chakra?" Zenitsu asked from the side, along with Xiao Zhuzhu Inosuke (Little Piggy Inosuke), who looked equally curious.
"Hehe~" Uchiha Nagi smiled faintly. Coming to this almost modern world and getting along so well with these younger brothers, his long-frozen heart had slowly melted a bit, so he didn't mind teaching them a few things.
"Chakra is this, watch closely, Shadow Clone Technique—"
Bang~
After a puff of smoke, several Uchiha Nagis appeared together in the living room, each one a solid Shadow Clone.
"Sugoi—" Zenitsu was the first to run over, touching Uchiha Nagi's Shadow Clone, then inspecting each one, finally confirming that it wasn't an illusion.
"Oh, oh—several mes? Haha, I win, I win..." Xiao Zhuzhu Inosuke (Little Piggy Inosuke), also curiously touched the Shadow Clones, then, not knowing what he was thinking, suddenly put his hands on his hips and burst into loud laughter.
"Want to learn? I'll teach you," Uchiha Nagi said with a smile.
"Yes, yes, we want to learn~" + 3.
The three sat in front of Uchiha Nagi like obedient children. Uchiha Nagi looked at Xiao Zhuzhu Inosuke (Little Piggy Inosuke). This guy didn't seem difficult to get along with; he probably hadn't interacted with others much, having grown up alone in the deep mountains since childhood. So, if someone was even a little kind to him, he could quickly become friends with them.
"Ahem, then I'll explain. Chakra is an energy produced by the perfect fusion of the various energy components controlled by the human body. It is the energy source for performing Ninjutsu, Genjutsu, Taijutsu, or for forming into threads to bind opponents or cut through objects also composed of Chakra.
And this energy is composed of: one, physical energy extracted cell by cell from the 130 trillion cells in the human body. Two, spiritual energy tempered through much training and accumulated experience."
"...?"
"What are cells?"
"What is spiritual energy??"
Inosuke even counted on his fingers and asked, "How much is 130 trillion? I only know one to ten."
Uchiha Nagi: "..."
It seemed like a long road ahead. Facing these three, who were worse than even a Ninja Academy kindergarten class, Uchiha Nagi felt a headache at the thought of teaching them how to extract Chakra.
However, the three were clearly very interested in the Shadow Clone Ninjutsu, which creates solid clones. Even if they didn't understand, they still sat steadily and listened attentively.
It wasn't until Tanjiro's sister, Nezuko, emerged from her wooden box that this scene was interrupted.
Even Uchiha Nagi was amazed by Nezuko's beauty, a combination of purity and loveliness, especially her innocent, adorable eyes, as pure as if she didn't belong to the mortal world, making anyone who saw her feel an urge to protect her.
However, it was merely a moment of astonishment. Uchiha Nagi was not someone who hadn't seen the world; as a transmigrator, he had seen countless beauties on the internet and quite a few in the Naruto World.
In contrast, the cowardly Zenitsu transformed into some kind of tengu, wagging his tail and running after Nezuko, which startled her. Xiao Zhuzhu Inosuke (Little Piggy Inosuke) on the side was also clearly a bit amazed by Nezuko, but he didn't know how to express it. The group spent a harmonious evening, full of chatter and noise. Uchiha Nagi also felt incredibly at ease, even accidentally falling into a deep sleep.
The next morning, when Tanjiro and the others opened their eyes, Uchiha Nagi was already practicing the Breathing Technique he had just learned in the yard.
"Beast Breathing, First Fang, Piercing Strike."
"Water Breathing, First Form, Water Surface Slash."
Two Shadow Clones, holding swords, fought each other, and Inosuke, who had just walked out, watched with a shocked expression.
"You... why do you know my Beast Breathing??"
Slap!
Zenitsu slapped Inosuke on the head. "Idiot, call him Nagi-aniki (Nagi, older brother), oh right, Tanjiro."
Tanjiro nodded. "Uchiha Nagi-aniki (Nagi, older brother), he can learn a Breathing Technique just by watching it once. He must have seen you use it in the demon house before, so he learned it."
"So... so amazing." Xiao Zhuzhu Inosuke (Little Piggy Inosuke) completely turned to stone and stood motionless.
"How are your injuries? If you're well, you can come and do morning exercises with my Shadow Clones. Don't worry about hurting me; a clone will just disappear if injured, and the main body will be fine," Uchiha Nagi said.
"Oh, oh, I'm fine! Then I'm coming, Nagi-aniki (Nagi, older brother)! Let's settle this, Pig Assault—" Xiao Zhuzhu Inosuke (Little Piggy Inosuke) roared, grabbed his two serrated nichirin blades, and charged forward.
Uchiha Nagi also wanted to learn more about this world's Breathing Techniques, so he had a Shadow Clone practice with him.
Tanjiro and Zenitsu also joined the morning training. They weren't using their full strength, just doing daily exercises, so the intensity wasn't too great, and they weren't worried about affecting their bodies.
Uchiha Nagi also intentionally held back to train the three. Their combat capabilities were too singular; letting them experience the Naruto World's fighting style would make it easier to improve their strength.
The three little ones, in terms of overall strength, were probably just Genin in the Naruto World. They couldn't use Ninjutsu, the Three-Body Technique, Genjutsu, or any tactics like poisoning strategies.
However, purely in terms of combat power, they might have the strength of a Jonin's Taijutsu, like Neji when he fought the Spider Man, and perhaps even surpassed it.
This was because the Breathing Technique was a versatile existence. In their long struggle against demons, the Demon Slayer Corps constantly used Breathing Techniques to counter unknown Blood Demon Arts, and continuously improved them.
With various bizarre Blood Demon Arts appearing, the Breathing Techniques gradually evolved to adapt and counter them.
It could be said that, without considering Genjutsu and secret techniques, Breathing Techniques could be perfectly versatile in countering Ninjutsu and Taijutsu in the Ninja World.